1. Field of the Invention
The present invention relates to a recording apparatus utilizing a magnetic linear encoder.
2. Related Background Art
For detecting the position or the amount of displacement of the carriage in a recording apparatus, there is generally employed a linear encoder, which has generally been known as the optical type and the magnetic type.
The optical linear encoder, based on optical reading of slits formed on a stripe-shaped scale, has been associated with drawbacks of reading errors in the case of dust deposition on the scale, and of the limitation in the precision of detection, because the pitch of the slits cannot be made small (minimum pitch being about 140 .mu.m) due to the restrictions on the process of forming slits on the stripe-shaped scale.
On the other hand, the magnetic linear encoder, relying on magnetic reading of magnetized portions of a magnetic material, has the features of being not influenced by the dust, also being capable of improving the precision of detection as the pitch of magnetization in the magnetized portions can be made smaller (minimum pitch being about 40 .mu.m), and showing faster response speed.
Such a magnetic linear encoder is recently attracting attention, as there have been developed magnetic materials that can be worked by pressing, drawing or scraping, and that are lower in cost.
FIG. 1 schematically shows a recording apparatus employing a conventional magnetic linear encoder. A recording head 1 generally contains an ink jet head and an ink tank in an integral manner, is preferably mounted in a the recording apparatus in detachable manner and is replaced by a new recording head unit when the ink in the ink tank is exhausted.
A carriage 2, supporting the recording head 1, is provided with a pin (not shown) engaging with a spiral groove of a lead screw 3, which is rotated, through a transmission mechanism (not shown), by a carriage motor (not shown) in the forward or reverse direction, whereby the carriage 2 is reciprocated in the directions a and b. An (magnetic resistance) element (not shown in FIG. 1) is provided in a magnetic head 12 for reading the magnetized portions of a scale 11.
A transport roller 4 advances a recording sheet 5 in a direction c, and the recording sheet 5 is intermittently transported during the recording operation. The magnetic head 12 is provided with a flexible printed circuit board 13 for extracting the output signal of the MR device in the magnetic head, and the circuit board is connected to a board 6 loaded on the carriage 2, by connecting a contact portion 14 to a connector (not shown).
In the conventional magnetic linear encoder employed in the recording apparatus, a magnetized scale, mounting members provided at the ends of the scale for mounting the scale to the main body of the recording apparatus, a magnetic head for detecting the magnetized portions, and a signal cable connected to the magnetic head are constructed in an integral manner.
Such a magnetic linear encoder is assembled to the main body of the recording apparatus by forming mounting holes on fixing members (side plates) at both sides of the main body, inserting both the ends of the scale into the mounting holes and applying a fixing pin from the outside of a fixing member.
More specifically, with reference to FIG. 2, the mounting members 21 fixed on both ends of the scale 11 are respectively inserted into holes formed on the fixing members (side plates) 10 of the main body of the recording apparatus, and then a fixing pin 29 is inserted in a gap between the fixing member 10 and the mounting member 21, whereby the scale is fixed to the main body.
Also, as shown in FIG. 3 which is a lateral cross-sectional view of the magnetic linear encoder employed in a recording apparatus, the magnetized portion 15 of the scale 11 is provided in an upper portion thereof and is read by the MR device 12a of the magnetic head 12.
The magnetized portion 15 of the scale 11 is not completely shielded from the outside.
In the above-explained fixing method, however, at the insertion of the ends of the scale into the holes of the fixing members 10, the magnetized portion may be damaged by the eventual contact with an end of the hole formed in the fixing member 10 or with the hand of the operator.
Also, at the fixation of the scale, because the magnetic head 12 and the signal cable (flexible printed circuit board) 13 mounted on the magnetic head are integrally constructed with the scale 11, there is required careful handling so that the fixing operation cannot be conducted efficiently.
Furthermore, since the scale is fixed, by the fixing pin 29, to the main body of the recording apparatus, the tension on the scale 11 cannot be maintained constant nor be regulated at a suitable value, so that the aid tension tends to fluctuate by the errors in the manufacture of the fixing members 10 and the scale 11.
Furthermore, in the conventional magnetic linear encoder, the magnetized portion positioned in the upper part of the scale is easily contacted by the hand of the user, thus being eventually damaged and losing the memory effect of the magnetization.
Also, the magnetized portion 15 of the scale 11 is not so constructed as to be completely shielded from the exterior, as mentioned above, so that fine particles such as paper dust may enter the gap between the magnetized portion 15 of the scale 11 and the magnetic head 12 thereby hindering proper detection or eventually destroying the magnetic head itself. Such fine particles are not limited to paper dust but also maybe dust generated from the surroundings, depending on the place of installation of the apparatus.
Also, in order to read the magnetized pattern of the magnetized portion 12 with the MR device 14, the air gap G therebetween, shown in FIG. 4, has to be maintained in the order of 10 .mu.m. The magnetic linear encoder has been inevitably expensive, as there are required a complex mechanism for ensuring the air gap G and adjustment therefor.
For avoiding these drawbacks, the magnetic material is formed as a wire, which is incorporated in a housing with the magnetic head formed in a bearing, thereby maintaining a constant air gap.
At the fixation of the wire-shaped scale in the recording apparatus, since appropriate positioning is difficult with a wire of having a circular cross section, the scale is given, at both ends, fixing members by which the positioning to the recording apparatus is achieved.
In such a conventional configuration, however, the additional fixing members for the scale increase the number of components and complicate the manufacturing process as they require a step of positioning and fixing the fixing members on both ends of the scale, thus constituting a factor of increased cost of the magnetic linear encoder.
Furthermore, the angle between the MR device of the magnetic linear encoder and the magnetized portion of the scale tends to increase by the addition of the above-mentioned fixing members and the addition of the fixing step.